1. Field of the Invention
The present invention relates to a power transmission system, such as for an electric automobile using an electric motor as a drive power source or an electric automobile using a fuel engine (an ordinary engine making use of an explosion of fuel) and an electric motor both as a drive power source, and to an operation method for the same.
2. Description of the Related Art
There is disclosed in Japanese Patent Application Laid-Open Publication No. 9-226394 a drive system 2001 for electric automobiles shown in FIG. 22.
The drive system 2001 for electric automobiles includes an electric motor 2003, a reduction gear set 2005, and a differential apparatus 2007.
The electric motor 2003 is driven by a vehicle-mounted battery to produce drive power, which is decreased in speed by the reduction gear set 2005 within a range of the number of revolutions of a travelling wheel and increased in torque, and resultant drive power is distributed via the differential apparatus 2007 to wheels.
In the drive system 2001, as shown in FIG. 22, the electric motor 2003 and the reduction gear set 2005 as well as this reduction gear set 2005 and the differential apparatus 2007 are connected directly with no clutch disposed on the way.
On the other hand, FIG. 23 shows an example of a power transmission system for a four-wheel driven vehicle having an ordinary engine as a drive power source.
This power transmission system includes a transversely arranged engine 2101, a transmission 2103, a belt-driving transfer 2105, a front differential 2107 (as a differential apparatus for distributing drive power from the engine 2101 to left and right front wheels), front axles 2109 and 2111, left and right front wheels 2113 and 2115, a rear-wheel end propeller shaft 2117, a coupling 2118, a rear differential 2119, rear axles 2121 and 2123, left and right rear wheels 2125 and 2127.
The drive power from the engine 2101 is transmitted from an output gear 2129 of the transmission 2103 via a ring gear 2131 to a differential case 2133, to be distributed from the front differential 2107 via the front axles 2109 and 2111 to the left and right front wheels 2113 and 2115, or to be transmitted via the differential case 2133m the transfer 2105, and the propeller shaft 2117 to the rear wheel end.
In this arrangement, the coupling 2118 disposed in a power transmission subsystem at the rear wheel end is employed for control of torque transmission to the rear wheels 2125 and 2127.
For example, when the coupling 2118 is connected, drive power from the engine 2101 is distributed from the rear differential 2119 via the rear axles 2121 and 2123 to the left and right rear wheels 2125 and 2127, rendering the vehicle four-wheel driven.
When the coupling 2118 is disconnected, the rear differential 2119 and subsequent elements of the rear wheel end subsystem are cut off, rendering the vehicle two-wheel driven.
In the conventional electric automobiles, an electric motor is connected directly to wheels, and even in a case of interruption of power supply to the electric motor, such as when travelling by inertia, the electric motor is forced to rotate together with wheel rotation, with burdens on the electric motor.
For example, if the electric motor is a brush type like a DC motor, brushes receive a great influence on the durability, resulting in increased maintenance costs, such as by increase in number of services for brush replacement.
Further, when caused to rotate by wheels, the electric motor serves as a generator, producing electromotive forces (emf). As the rotation is increased in speed by the reduction gear set, there is produced a greater emf, resulting in burdens, such as on a battery or alternator (not shown) or on circuit elements such as a regulator constituted as an integrated circuit, causing a reduced durability.
The present invention is made with such points in view. It therefore is an object of the present invention to provide a power transmission system with a compact size, light weight, and well adaptation for vehicle-mounting, preventing an electric motor from being caused to rotate by rotation of wheels, and an operation method for the same.
To achieve the object, according to a 1st aspect of the invention, there is provided a power transmission system comprising a speed reducing mechanism for speed-reducing drive power of an electric motor, a differential apparatus for distributing speed-reduced drive power to axle ends, and a clutch configured for interruptive transmission of drive power between the speed-reducing mechanism and the differential apparatus.
Accordingly, in case power supply to the electric motor is interrupted, such as when travelling by inertia, connection of the clutch is canceled, thereby disconnecting the electric motor from wheels.
Thus, the electric motor is set free from being rotated by rotation of the wheels, and kept from generating emf that otherwise might have imposed loads on a battery, alternator, or controller""s circuit elements, allowing these to have maintained performances, with a greatly improved durability.
Because mechanical rotation is prevented, burdens on and temperature rise of magnetic field or rotor side windings of the electric motor are reduced, as well as burdens on bearings, with a greatly improved durability.
In case of a brush type electric motor, such as a DC motor, the brushes have greatly improved durability, with a commensurate reduction in frequency of their replacement, with reduction of maintenance cost.
According to a 2nd aspect second aspect of the invention, a power transmission system according to the 1st aspect further comprises a main drive power source, and the electric motor used as an auxiliary drive power source relative to the main drive power source.
Accordingly, in a four-wheel driven vehicle using both a main drive power source (engine) and an electric motor, when the electric motor is rotated with the clutch in connection, the vehicle enters a four-wheel driven state with improvements such as in abilities of start, acceleration, and riding performances such as on differences in level or cavities in road.
In a two-wheel driven travel at the engine side, or upon occurrence of a rollback by front wheels idling such as on an inclined road low of surface frictional resistance in a four-wheel driven travel, the clutch is disconnected to interrupt connection between the electric motor and wheels, whereby the electric motor is kept from being rotated by rotation of wheels, allowing for like effects to the 1st aspect to be achieved.
According to a 3rd aspect of the invention, in a power transmission system according to the 1st or 2nd aspect, the speed-reducing mechanism comprises a plurality of reduction gear sets including a first reduction gear set for inputting thereto drive power from the electric motor, the first reduction gear set comprising a planetary gear, whereby like effects to the 1st or 2nd aspect are achieved.
In addition, by use of the planetary gear in the first reduction gear set, the speed-reducing mechanism which is constituted with a plurality of stages can be made small in size.
In particular, in the case the electric motor is used as an auxiliary drive power source relative to the main drive power source, the input from the electric motor to the speed-reducing mechanism is has a smaller value than a case the electric motor is used as a main drive power source, and the arrangement in which the first reduction gear set is constituted with the planetary gear allows an efficient reduction in size of the speed-reducing mechanism.
According to a 4th aspect of the invention, in a power transmission system according to the 3rd aspect, the speed-reducing mechanism is provided with an oil pump for supplying lubricant to the planetary gear, whereby like effects to the 3rd aspect can be achieved, in addition to effective lubrication of the planetary gear, possible reduction of meshing resistance of the planetary gear, and preventive gnaw of gears.
According to a 5th aspect of the invention, in a power transmission system according to the 4th aspect, the oil pump is provided on a lid side of a case, whereby like effects to the 4th aspect can be achieved.
In addition, oil pump can be machined and mounted with ease, and a lid part of the case can be used as part of the oil pump to constitute an tight-closed part, with a simplified structure.
According to a 6th aspect of the invention, in a power transmission system according to any of the 1st to 5th aspects, the speed-reducing mechanism comprises a plurality of reduction gear sets, and the clutch is disposed in a power transmission path of the speed-reducing mechanism, whereby like effects to the 1st to 5th aspects can be achieved.
In addition, this arrangement in which the clutch is disposed in a power transmission path of the speed-reducing mechanism allows, for example, a selected clutch to be disposed in a place optimal of speed reduction ratio in accordance with the type and capacity, or an optimal clutch to be selected in accordance with sliding speed or transmitting torque of reduction gears, and the like.
Like this, flexibility of design can be increased with respect to the place for disposition of the clutch, as well as to the clutch selection.
According to a 7th aspect of the invention, in a power transmission system according to the 6th aspect, the speed-reducing mechanism and the differential apparatus are neighbored to each other, and the clutch is coaxially provided to one of the plurality of reduction gear sets of the speed-reducing mechanism that is nearest to the differential apparatus, whereby like effects to the 6th aspect can be achieved.
In addition, because the clutch is coaxial to one of reduction gear sets of the speed-reducing mechanism that is nearest to the differential apparatus, the clutch can be arranged within a projection area of large-size parts, such as a ring gear of the differential apparatus, allowing the system to be entirely compact in size.
According to an 8th aspect of the invention, in a power transmission system according to any of the 1st to 7th aspects, the speed-reducing mechanism and the differential apparatus are integrally arranged in a casing, whereby like effects to the 1st to 7th aspects can be achieved.
In addition, because the clutch is integrated with the speed-reducing mechanism and the differential apparatus, the power transmission system can be the more light-weighted, compact in size, and improved in vehicle-mountability.
Further, since the speed-reducing mechanism is integrated with the differential apparatus, the amount of oil to be supplied to the clutch is increased, allowing sufficient lubrication and cooling, and greatly improved durability, permitting a normal use to be near 100-% capacity.
Along therewith, the clutch can be made smaller in size, allowing the power transmission system to be the more light-weighted and compact in size.
According to a 9th aspect of the invention, in a power transmission system according to the 8th aspect, a final reduction gear set and a previous reduction gear set relative thereto are axially neighbored to each other, whereby like effects to the 8th aspect can be achieved.
In addition, reduction gear can have a shorter support span, allowing adequate meshing of the gear, reduced vibration, and enhanced durability.
According to a 10th aspect of the invention, in a power transmission system according to the 9th aspect, the previous reduction gear set is disposed on an axially one side of the final reduction gear set, and the differential apparatus is disposed on an axially opposite side of the final reduction gear set, whereby like effects to the 9th aspect can be achieved.
In addition, the casing which has the final reduction gear and the differential apparatus incorporated therein can have a controlled weight balance in a vehicle-transverse direction.
According to an 11th aspect of the invention, in a power transmission system according to the 10th aspect, the clutch is coaxially neighbored, at an axially outer side, to the differential apparatus, whereby like effects to the 10th aspect can be achieved.
In addition, the casing can have a controlled weight balance in a vehicle-longitudinal direction also. Further, for the clutch to be set hardly receives restriction due to interference with peripheral members, flexibility of design is enhanced, such as in clutch capacity, clutch configuration, and condition for installation of an actuator.
According to a 12th aspect of the invention, in a power transmission system according to the 7th or 8th aspect, the plurality of reduction gear sets of the speed-reducing mechanism is provided near a differential center of the differential apparatus, whereby like effects to the 7th or 8th aspect can be achieved.
In addition, because the reduction gear sets are arranged near the differential center of the differential apparatus, an entirety of power transmission system including the differential apparatus and the speed-reducing mechanism can be well-balanced.
In particular, in case the differential apparatus and the speed-reducing mechanism are separately fabricated and disposed to be adjacent with each other, a joint part between the differential apparatus and the speed-reducing mechanism is free from undue extra forces, as an advantage in strength, as well.
According to a 13th aspect of the invention, in a power transmission system according to any of the 1st to 8th and 12th aspects, the clutch comprises a frictional clutch, whereby like effects to the 1st to 8th and 12th aspects can be achieved.
In addition, this arrangement of power transmission system is allowed to arbitrarily control transmission torque by regulating pressing forces of the frictional clutch.
Further, the use of a frictional clutch eliminates generation of ratchet sounds such as in meshing clutch for example, and high of calmness.
The use of a frictional clutch eliminates shocks and shock sounds in clutch connection and cancellation thereof.
The frictional clutch does not need synchronization of rotation in clutch connection and cancellation thereof, and can be fabricated at the lower cost.
According to a 14th aspect of the invention, in a power transmission system according to the 13th aspect, the frictional clutch comprises a multi-plate clutch, whereby like effects to the 13th aspect can be achieved.
In addition, this arrangement of power transmission system using a multi-plate clutch is allowed to handle large drive power, because the multi-plate clutch can use wide frictional surface areas to obtain a sufficient capacity even if compact in size.
Moreover, by making the multi-plate clutch compact, the power transmission system can be the more light-weighted, compact in size, and improved in vehicle-mountability.
Further, because the clutch plates can be easily changed in number and diameter to thereby adjust the capacity, there is great flexibility in design.
According to a 15th aspect of the invention, in a power transmission system according to the 13th aspect, the frictional clutch comprises a cone clutch, whereby like effects to the 13th aspect can be achieved.
In addition, because the cone clutch is simple in structure and small of components, the power transmission system can be the more light-weighted, compact in size, improved in vehicle-mountability, and reduced in cost.
According to a 16th aspect of the invention, in a power transmission system according to any of the 1st to 8th and 12th aspects, the clutch comprises a meshing clutch, whereby like effects to the 1st to 8th and 12th aspects can be achieved.
In addition, because the meshing clutch is free from dragging torque due such as to viscosity of oil, unlike the frictional clutches, the loss of drive power is little, allowing for the electric motor to be improved in durability.
Because of unnecessary countermeasures such as lowering oil viscosity, raising temperature, and reducing amount of oil for the dragging torque to be reduced, implementation can be the more reduced in cost.
Moreover, when the clutch is disconnected, the electric motor is not mechanically rotated by dragging torque, protection performances such as of a battery, alternator, and circuit elements can be improved, as well as durability of the electric motor.
Further, this arrangement of power transmission system employs a meshing clutch which can provide a compact size with a great capacity, allowing for great drive power to be handled.
Still more, because the meshing clutch is simple in structure and small of component number, the power transmission system can be the more light-weighted, compact in size, and improved in vehicle-mountability, with a low cost.
According to a 17th aspect of the invention, in a power transmission system according to the 16th aspect, the meshing clutch comprises a dog clutch, whereby like effects to the 16th aspect can be achieved.
In addition, because the dog clutch does not need connection members such as coupling sleeve to be moved between meshing teeth for engagement or disengagement, the structure is by far simple and low of cost. Moreover, as a narrow installation space can do, this arrangement of power transmission system is allowed to have a clutch portion the more simplified in structure, reduced in cost, and compact in size.
According to an 18th aspect of the invention, in a power transmission system according to any of the 1st to 8th and 12th aspects, the clutch comprises a one-way clutch, whereby like effects to the 1st to 8th and 12th aspects can be achieved.
In addition, when connection is canceled, the one-way clutch is free from rotational resistance such as by dragging torque in frictional clutch, and in this arrangement of power transmission system using a one-way clutch, the electric motor in a stopped state is prevented from being rotated, with the more improved durability.
Because the one-way clutch does not need an operation mechanism nor control mechanism therefor, the above arrangement of power transmission system is the more simplified, light-weighted, and compact in size.
By use of a small-sized lightweight one-way clutch, the above arrangement of power transmission system can be more light-weighted and compact.
Further, in application such as to a four-wheel driven electric automobile using an electric motor as an auxiliary drive power source, the one-way clutch may be arranged to be connected when the vehicle runs forward, so that upon rotation of the electric motor associated wheels are driven via the one-way clutch, allowing for the vehicle to have improved abilities such as when starting or in acceleration, or to run over differences in level, cavities in road, etc.
Still more, when rotation of the electric motor is stopped, the vehicle enters a two-wheel driven state. In this state, connection of the one-way clutch is canceled by preceding rotation of associated wheels, of which rotating actions otherwise might have forced the electric motor to rotate, but now are isolated from the electric motor.
Like this, the electric motor is prevented against such forced rotation, to be free from burdens that otherwise might have been imposed to produce emf, such as on a battery, alternator, circuit elements, etc., and is allowed to have an enhanced durability.
According to a 19th aspect of the invention, in a power transmission system according to any of the 1st to 8th and 12th aspects, the clutch comprises a two-way clutch in which canceling directions of relative rotations are switchable, whereby like effects to the 1st to 8th and 12th aspects can be achieved.
In addition, in this arrangement of power transmission system using a two-way clutch, the electric motor can be prevented from being forced to rotate by wheels, in both forward run and backward run.
Therefore, it can cope with a rollback of the vehicle, allowing for enhanced protection to be effected, such as of the electric motor, a battery, an alternator, associated circuit elements, etc.
Unlike the case of using a one-way clutch that needs another clutch for backward run and an extra controller for necessary connection in the backward run and disconnection for forward run, the above arrangement of power transmission system using a two-way clutch, coping also with backward run as described, does not need the clutch for backward run nor the extra controller, and is allowed to be the more simplified in structure, light-weighted, compact, and improved in vehicle-mountability, with a low cost.
Further, this arrangement of power transmission system has like effects to the 18th aspect using a one-way clutch.
According to a 20th aspect of the invention, in a power transmission system according to any of the 1st to 8th and 12th aspects, the clutch comprises a centrifugal clutch, whereby like effects to the 1st to 8th and 12th aspects can be achieved.
In a four-wheel driven electric automobile employing both a main drive power source (engine) and an electric motor, the centrifugal clutch is disposed on a driving end, and the electric motor is controlled so as to start when the centrifugal clutch is connected.
When the vehicle is stopped (to start) or when the vehicle speed is decreased so that wheel revolution speed becomes lower than a critical value, the centrifugal clutch is connected, and the electric motor is started, driving wheels via the centrifugal clutch, rendering the vehicle four-wheel driven.
If the vehicle speed is increased so that the wheel revolution speed reaches critical value, the centrifugal clutch is operated for clutch cancellation, when rotation of the electric motor is stopped to render the vehicle two-wheel driven from the engine.
Like this, because forced rotation by the vehicle is isolated from the electric motor by use of the centrifugal clutch, the electric motor is prevented against such forced rotation, to be free from burdens that otherwise might have been imposed to produce emf, such as on a battery, alternator, circuit elements, etc., and is allowed to have an enhanced durability.
In addition, when the connection is cancelled, as the centrifugal clutch is free from rotational resistance unlike the frictional clutch subjected to dragging torque, the above arrangement of power transmission system using a centrifugal clutch have the more improved effects, such as on fuel consumption (when two-wheel driven) with rotation of the electric motor stopped, or on durability of the motor.
In addition, in this arrangement of power transmission system using a centrifugal clutch, the electric motor can be kept from being forced to rotate by wheels, in both forward run and backward run, permitting effective protection such as of battery, alternator, and circuit elements.
Because the centrifugal clutch does not need an operation mechanism nor control mechanism therefor, the above arrangement of power transmission system is the more simplified, light-weighted, and compact in size.
By use of a small-sized lightweight centrifugal clutch, the above arrangement of power transmission system can be more light-weighted and compact, allowing for great drive power to be handled.
Further, to achieve the object described, according a 21st aspect of the invention, there is provided an operation method for a power transmission system according to any of the 16th to 20th aspects, the method comprising the step of canceling connection of the clutch, switching a rotating direction of the electric motor, thereby causing a contact portion of the clutch to vibrate so that the contact portion has a reduced frictional resistance.
Like this, when canceling connection of the clutch, the direction of rotation of the electric motor is switched to give vibration to a contact portion of the clutch so that the contact portion has a reduced frictional resistance, thereby allowing connection and cancellation, such as of a meshing clutch, one-way clutch, two-way clutch, or centrifugal clutch, to be properly effected, when intended, or at a predetermined vehicle speed.
Like this, there can be maintained protection functions to be high, such as of an electric motor, battery, alternator, and circuit elements in a power transmission system according to any of the 16th to 20th aspects.
Further, a four-wheel driven state of the vehicle can be changed to a two-wheel driven state, as necessary, with enhanced maneuverability.
According to a 22nd aspect of the invention, there is provided an operation method for a power transmission system according to any of the 16th to 20th aspects, the method comprising the step of canceling connection of the clutch, changing a revolution number of the electric motor so that a contact portion thereof has a reduced frictional resistance, whereby like effects to the 21st aspect can be achieved.